Wheel cylinders for drum brakes are difficult to replace because no suitable tool exists for pressing a retainer clip into place.
A brake cylinder for drum-type brakes is mounted below the brake shoe retraction spring retainer on a brake backing plate fixed on an end of an axle housing. Typically, a brake cylinder has two pistons which move outwardly to apply brakes. Brake fluid is supplied between the pistons in the cylinder through a cylinder mounting projection. The mounting projection extends through an opening in the brake mounting plate. A circular steel clip is connected to the projection, anchoring the cylinder on the plate. A conventional retaining clip has a warped circular periphery with two radially opposed prongs which extend inward from opposite high points on the circle. The clip is made of spring steel. When the clip is pushed downward over the brake cylinder mounting projection the prongs are ramped outward. When the retainer is fully installed and the high points of the circle are flattened against spring force in the clip, ends of the prongs snap inward and engage shoulders on the cylinder mounting extension. With the ring of the retainer resting against the back of the brake mounting plate, the ends of the prongs are pressed inward against the shoulders, holding the cylinder mounting extension firmly in the plate, and holding the cylinder firmly against the outer side of the plate, in brake actuating position.
When it is necessary to remove and replace the cylinder, the retainer clip prongs are spread outwardly, and the cylinder mounting extension slides easily through the plate as the cylinder is removed.
Replacement of the cylinder is relatively easy. The projection on a new cylinder is slid through the brake plate on the axle housing in the opening provided for that purpose. Installation of a new retainer clip is difficult. While an outside force is holding the brake cylinder inwardly, the retainer clip must be pushed outwardly in the opposite direction to spread the prongs and snap the prongs under the shoulders of the mounting projection. The forces are substantial.
The retainer clip, which is made of spring steel is about 1/16" thick, has an outer diameter of about 1/2" and an inner diameter of about 1/4", has two diametrically opposed retainer prongs which extend inward about 5/16" and which have bases about 1/4" wide attached to the inner diameter of the ring, and which are about 5/16" wide at their flat inner ends. The flat inner ends of the prongs are flexed outward over ramps near the outer end of the mounting extension and rebound inward to engage shoulders under the ramps. Portions of the ring, which are 90.degree. offset from the prongs, engage the inside of the brake backing plate. The rings of the retainer clips are warped so that the portions from which the prongs extend are urged by spring force away from the backing plate. As a consequence, spring forces urge the prongs inward and at the same time urge the prongs away from the backing plate. Ends of the prongs engage the shoulders of the cylinder mounting extension while the 90.degree. offset portions of the rings are pressed against the backing plate. The spring force is substantial since it locks the cylinders in position. Substantial excessive force must be provided by the retainer clip to prevent unwanted dislodgement of the cylinder when an automobile is subjected to vibrations and shock.
When installing the retainer spring two substantial forces are required, the force to spread the prongs outwardly over the ramps and the force to deform the ring. The application of both of those forces tends to press the cylinder body away from the brake mounting plate and makes the affixation of the retainer clip extremely difficult. When using screwdrivers, for example, premature release of the clip may result in a violent projecting of a clip from its intended location, propelling the clip through space, and bouncing the clip off hard surfaces, with attendant danger to a mechanic.
Two screwdrivers are often used, which promotes frustration of the mechanic. The screwdrivers may do damage to the axle housing end plate, which is also called the brake backing plate. Much time is required, and the possibility of injury to the mechanic because of the forces applied and the spring nature of the retainer is ever present. Visual and manual access to the upper inside of the backing plate is difficult, which adds to the problem.
Many problems remain. The present invention is directed to solving the problems of applying a wheel cylinder retainer clip when installing a wheel cylinders.